1. Field of the Invention
A great many of small ball-shaped metallic particles are widely used for soldering or powder metallurgy. A number of methods and devices for producing particles of this type from a molten metal are known. For example, particles of liquid metal are produced by means of dissecting liquid metal above a gas stream flowing against the force of gravity, wherein the particles adopt a ball shape due to the surface tension of the liquid metal and solidification.
In another method, a metallic wire or plate is cut into pieces, each having a given length, which are pressed and rolled into small metallic particles, or alternately the cut pieces are melted and the molten metal is rolled into small metallic particles.
The small ball-shaped metallic particles thus produced have the disadvantage that there is a difference of the melting temperatures of the small metallic particles made from the starting material made from an end portion and that of a middle portion thereof.
As a result, there is a tendency that when spontaneous soldering of semiconductor circuits is carried out at a determined temperature, some portions of the circuits are not soldered.
It is likely that some metallic particles are either deformed or their surfaces are damaged.
A good small ball-shaped metallic particle usually has a brilliant metallic luster on its surface so that the quality of the produced metallic particle can be judged by quality of the luster of the small ball-shaped metallic particle as its standard.
2. Description of the Prior Art
According to the recent method described in the published specification of Japanese Patent Publication No. 43794/1987 (not-examined), molten metal is sprayed into the air. As shown in the published specification of Japanese Patent Publication No. 184201/1988, the method of producing the small ball-shaped metallic particles is shown, in which a molten stream of metal flows under pressure through an opening of a container in order to produce the small ball-shaped metallic particles under the surface tension.
There is a tendency, however, for the above method to produce a lot of either deformed or damaged small ball-shaped metallic particles, thus providing a lower yield. Accordingly, it is rather difficult to efficiently produce a number of good small ball-shaped metallic particles.
As shown in the published specification of Japanese Patent Publication No. 144216/2000 (not-examined), liquid metal is discharged through an opening of a container to atomize in the air and to solidify into droplets by the surface tension of the liquid metal.
In accordance with this method, however, liquid metal particles are dropped into an oily solution which does not vaporize even at 200xc2x0 C. in order to prevent collision of the dropping small particles with each other or to avoid a deformation by a shock on a hard bottom plate.
This method, however, has the disadvantage that the metallic surfaces of the produced metallic particles are oxidized by the oily solution, thereby preventing an independent brilliant metallic luster on the surfaces of the produced small ball-shaped metallic particles.
A primary object of this invention is to provide a method for producing small ball-shaped metallic particles substantially equal in diameter that can be used for soldering a base circuit of semiconductors.
Another object of this invention is to provide a device for producing small ball-shaped metallic particles substantially equal in diameter that can be used for soldering a base circuit of semiconductors.
Another object of this invention is to provide a device for producing small ball-shaped metallic particles substantially equal in diameter having better physical, structural and homogeneous properties.
Another object of this invention is to provide a method for producing small ball-shaped metallic particles substantially equal in diameter without a troublesome washing process for recovering the metallic particles in an oily solution.
Another object of this invention is to provide a method for producing small ball-shaped metallic particles substantially equal in diameter without a troublesome disposal of waste oil.
Another object of this invention is to provide an easily made device, which is simple in construction.
Another object of this invention is to provide a method for producing small ball-shaped metallic particles substantially equal in diameter whereby soft droplets drop on a soft inclined bottom plate, thus eliminating dents, flaws or deformations on the surface of the metallic particles as a result of cushioning of the soft inclined bottom plate.
Still another object of this invention is to provide small ball-shaped metallic particles substantially equal in diameter.